The present invention relates to a method for producing a cordierite body.
Cordierite (2MgO.2Al.sub.2 O.sub.3.5SiO.sub.2) has excellent low thermal expansion and is a suitable material to produce a product required to have thermal shock resistance when subjected to repeated cycles of rapid increases and decreases in temperature, for example a honeycomb structured catalyst support for purifying exhaust gas.
The coefficient of thermal expansion of cordierite has been generally known as 26.0.times.10.sup.-7 /.degree.C. in the range of 25.degree. to 1000.degree. C.
Recently, various studies have been made to obtain a cordierite body having a more excellent thermal shock resistance. As a result, it has been found that by eliminating alkali metals such as sodium and potassium, alkaline-earth metals such as calcium and other impurities having an adverse effect on the low thermal expansion of cordierite, from the material, a cordierite body having a thermal expansion property as low as 17.0.times.10.sup.-7 /.degree.C. in the range of 25.degree. to 1000.degree. C. can be obtained.
Furthermore, it has been reported that by orienting the anisotropic property of the cordierite crystals, cordierite bodies having coefficients of thermal expansion of less than 11.0.times.10.sup.-7 /.degree.C. in the range of 25.degree. to 1000.degree. C. in at least one direction can be obtained.
For example, one of the methods for orienting the cordierite crystals to reduce the thermal expansion of the cordierite body in at least one direction is shown in U.S. Pat. No. 3,885,977.
In U.S. Pat. No. 3,885,977, it is stated that a cordierite body having a thermal expansion as low as 11.0.times.10.sup.-7 /.degree.C. is obtained by forming a batch raw material containing plate-shaped particles, particularly kaolinite particles such as imparting a planar orientation to the plate-shaped particles, for example extrusion forming, drying and firing the obtained formed body.
One object of the present invention is to provide a cordierite body having a lower coefficient of thermal expansion in a specific direction compared with the conventional cordierite bodies.
Another object of the present invention is to provide a method for producing a cordierite body having the above described property with good productivity.
Still another object of the present invention is to provide a method for producing a cordierite body having the above described property without generating any shrinkage in the firing process.
Further object of the present invention is to provide a cordierite honeycomb structure having excellent thermal shock resistance, in particular to provide a honeycomb structure for use as a catalyst support for purifying exhaust gas of a vehicle.